The present application relates to oil well servicing and in particular to a method and apparatus for the removal and prevention of paraffin buildup within oil well tubing.
The accumulation of paraffin within the production string of a working oil well is a major problem experienced throughout the oil industry. The paraffin content of crude oil varies greatly between different geographic regions. However, virtually all crude oil contains a sufficient paraffin content that will result in an accumulation of solidified paraffin within the production string of the oil well. The rate of paraffin buildup varies between different wells, but virtually all oil wells experience paraffin accumulation to a degree that requires periodic servicing of the well to remove the paraffin accumulation. If not serviced, the paraffin buildup gradually restricts the oil well output to a very small percentage of its potential output and eventually may shut off oil flow completely.
Heretofore, the servicing of an oil well to remove paraffin accumulation typically required a complete pulling of the production tubing, sucker rod and pump. A transportable workover rig is driven to the well site and used to pull the entire production string section-by-section. New tubing and sucker rod strings are lowered into the well in order to reduce the down time of the well during makeover or servicing. The paraffin restricted sections of tubing and sucker rod are placed in a hot bath in order to melt and remove the paraffin, and then replaced in another oil well. The workover of an oil well is a relatively expensive and time consuming operation, particularly for deep wells having lengthy production strings. Another popular method of removing paraffin is a "hot oil or water treatment". This method involves taking a truck loaded with hot oil or water to the well site and pumping the hot liquid down the anulus and back up the production string, so that the paraffin, which is consequently melted, can be pumped out of the well.
Various attempts have been made to avoid the high cost of working over an oil well by the proposed use of electric heating to reduce paraffin accumulation. In such proposed methods, electrical current is applied to the oil well casing and tubing to result in a heating of those elements. One problem with such systems resides in the fact that the paraffin accumulation occurs within the tubing. Any heating occurring in the casing has a reduced effect on the accumulated paraffin due to the physical separation between casing and tubing and the insulating effect of air or oil therebetween. Another problem associated with such systems are energy losses that occur outwardly from the heated casing into the surrounding earth. It has been found that typical earth formations in the vicinity of oil reserves such as sandstone and the like are relatively good heat conductors. Still another problem resides in the fact that the casing quite often does not extend down the entire length of the well in wells referred to as a "rat hole well". Quite often the casing terminates a substantial distance above the bottom of the well and may be removed from the problematic paraffin accumulation. In all oil wells the well casing must be cemented in. As a result of various problems, such prior casing heating systems have not been accepted in the oil industry.